The present invention relates to a composite member fixing structure, and more particularly, to a fixing structure, for example, in a vehicle engine, which structure fixes a composite member, which includes a synthetic resin cylinder head cover and a metal housing of an oil control valve, to a coupled member such as a cam cap arranged on a cylinder head.
Conventionally, for example, Japanese Laid-Open Patent Publication No. 2007-107479 (first prior art) and Japanese Laid-Open Patent Publication No. 2007-100657 (second prior art) disclose this type of composite member fixing structure.
According to the fixing structure of the first prior art, a composite member is formed by insert molding a metal oil control valve housing (hereinafter, simply referred to as OCV housing) into a synthetic resin cylinder head cover. A bolt insertion hole is formed in the composite member, and an internal thread is formed in a cam cap on a cylinder head. Through the bolt insertion hole, a bolt is screwed into the internal thread, so that the composite member is fixed to the cam cap. On an outer circumferential surface of the composite member located outside of the bolt insertion hole, a groove is formed in a surface of the OCV housing that contacts the cylinder head cover. The groove extends along the outer circumferential surface of the OCV housing, and is filled with adhesive. When insert molding the composite member, resin flows into the groove so that the resin is adhered to the inside of the groove by the adhesive. Accordingly, the adhesive seals the gap between contacting surfaces of the cylinder head cover and the OCV housing.
According to the fixing structure of the second prior art, a composite member is formed by assembling a metal OCV housing to a synthetic resin cylinder head cover. The OCV housing includes a boss having a bolt insertion hole, and the cylinder head cover includes a cylindrical portion that is fitted about the outer circumferential surface of the boss. Through the bolt insertion hole, a bolt is screwed into an internal thread of a cam cap on the cylinder head, so that the composite member is fixed to the cam cap. An annular sealing member is provided between the outer circumferential surface of the proximal portion of the boss and the inner circumferential surface of the cylindrical portion. The sealing member is located on the outer circumferential surface of the boss, which has the bolt insertion hole, and seals the gap between the contacting surfaces of the cylinder head cover and the OCV housing.
The fixing structures of these prior arts have the following drawbacks.
According to the fixing structure of the first prior art, the insert molding of the composite member is performed with the groove on the OCV housing filled with the adhesive. Therefore, when molding the composite member in a mold, the flowing pressure of synthetic resin injected into the mold is likely to cause the adhesive to leak from the groove. In such cases, it is difficult to obtain a desired sealing. In addition, adhesive that leaks out from the groove reaches the outer surface of the cylinder head cover, and contaminates the outer surface. In other cases, adhesive that leaks at the molding contaminates the molding surface of the mold.
According to the fixing structure of the second prior art, the cylinder head cover and the OCV housing of the composite member are assembled together in a process after molding. The assembly requires a process for placing a sealing member between the contacting surfaces of the cylinder head cover and the OCV housing. This makes the assembling procedure troublesome and time consuming.
In each of the fixing structures of the first and second prior arts, sealing is provided on the outer circumferential surface of the boss, which has a bolt insertion hole, and between the contacting surfaces of the cylinder head cover and the OCV housing. However, no sealing is provided between the inner circumferential surface of the bolt insertion hole and the outer circumferential surface of the bolt shank. Therefore, oil leak easily occurs through the gap between the inner circumferential surface of the bolt insertion hole and the outer circumferential surface of the bolt shank.